The value of quantitative ultrasound tissue characterization of the cervix and rapid fetal fibronectin in predicting preterm delivery

Abstract

To evaluate clinical risk factors, cervical fetal fibronectin (fFN), cervical length, and mean gray value assessment in predicting of preterm delivery (PTD) in patients with signs and/or symptoms of preterm labor (PTL). One hundred and seventeen women with PTL between 24 and 34 weeks of gestation were included. Cervical swabs were tested for fFN using the rapid fFN assay. When 2-dimensional transvaginal ultrasound measurement of cervical length was completed, a region of interest (ROI) of constant size was defined in the midsection of the posterior wall, and the tissue-specific gray scale was determined. The end point were PTDs at <34 and <37 weeks of gestation. In univariate analysis, the three strongest predictors of spontaneous preterm birth <34 weeks were positive fFN (relative risk [RR] 8.9; 95% confidence interval [CI] 2.6-30.1), cervical length < or =2.5 cm (RR 6.9; 95% CI 1.6-29.7), and a low mean gray value of < or =5.97 (RR 7.9; 95% CI 2.3-27.2). Predictors significantly associated with spontaneous PTD at less than 37 weeks of gestation included previous PTD in multiparas (RR 3.9; 95% CI 1.6-9.5), positive fFN (RR 7.6; 95% CI 3.8-15.3), cervical length < or =2.5 cm (RR 2.6; 95% CI 1.4-5.1) and a low gray scale value of < or =6.54 (RR 4.5; 95% CI 2.3-8.9). In the final regression models used to predict spontaneous PTD <34 weeks and <37 weeks of gestation, both a positive fetal fibronectin (odds ratio [OR] 13.4; 95% CI, 2.5-72.1, P=0.003 vs. OR, 17.3; 95% CI 4.9-61.8, P<0.001) and a low gray scale value (OR 6.3 95% CI 1.3-29.4, P=0.02 vs. OR, 7.1; 95% CI 2-25.2, P=0.003) remained powerful predictors. The RRs of spontaneous PTD <37 weeks has been analyzed by a combination of these significant parameters. Low mean gray value < or =6.54 and negative fFN had a 10.3-fold (95% CI 2-74.5) increased risk of spontaneous preterm birth at <37 weeks. Combination of positive fFN and normal gray level (>6.54), had a higher increase risk of PTD (RR 18.1; 95% CI 4.4-76.7). When both factors were positive, the RR increases to 24.8 (95% CI 6.2-98.7). Combined use of rapid fFN and cervical gray value analysis improves the diagnostic efficiency and allows identification of women at risk for preterm delivery and in need for further prophylactic/therapeutic intervention.